ITA!!
And if you're judging "average" by Cartier, then you're running in different circles than I am, my friend. Everyone *I* know, myself included, knows someone in the diamond business and didn't buy their e-rings for much above cost. I don't think I know anyone with branded e-rings (although a lot of people go for the branded wedding bands); most people I know (again, me included) have commissioned pieces from jewelers that are connected through family ties. And if you walk down 47th, you'll see a LOT of REALLY. BIG. ROCKS.....just like you will at Graff. Cartier seems like a very strange standard by which to measure "average";.
Yes, if you are comparing a brand name (which is what you are paying for) then you will be paying up the wazoo. I was in Monte Carlo at Cartier around the time I was getting engaged and they had an amazing pink oval 3ct diamond ering. Talk about sticker shock. $1.7 million USD. Most people I know have friends/family in the jewelry business and you get good prices. My jeweler searched out stones for my ring after we told him what I wanted.